1. Field of the Invention
This invention relates to a maintenance signal corresponding to a mini slot signal in a slot according to international standard ITU-T G.983.1 regulating a physical interface in a PON (Passive Optical Network) and a method for controlling a state in dynamic bandwidth assignment (DBA) for upstream by using the mini slot signal.
2. Description of the Related Art
FIG. 3 illustrates an example of a configuration of a system in the PON including a DBA function, in which an OLT (optical line terminator—parent station) 101 and a plurality of ONU's (optical network terminating units—child stations) 102-104 are coupled to by a star coupler 105. FIG. 4 illustrates a downstream frame format 151 and an upstream frame format 152 in the PON according to international standard ITU-T G.983.1 regulating a physical interface in the PON according to the related art. FIG. 5 shows a state transition table for managing a state of an individual ONU dealing unit in the OLT according to international standard ITU-T G.983.1 regulating an operation by the OLT for controlling starting and halting of an individual ONU. FIG. 6 illustrates an example of a condition of detecting and resetting according to international standard ITU-T G.983.1 related to a maintenance signal provided for each of the ONU's indicating a state of receiving an ATM (asynchronous transfer mode) cell and PLOAM (Physical Layer Operation Administration and Maintenance) cell in an upstream frame in the OLT. Further, FIG. 7 illustrates a format of a mini slot in a slot according to international standard ITU-T G.983.1 related to the upstream frame.
In FIG. 3, the OLT 101 includes an individual ONU dealing unit 106B, a generator 107 for downstream frame, a controller 108 for upstream band, a DBA controller 109B, a terminator 110 of upstream frame, and a terminator 111 of mini slot. The ONU 103 includes a terminator 112 of downstream frame, a detector 113 for upstream band, a cell buffer 114 for upstream, a monitor 115 for buffer state, and a cell generator 116 for upstream.
With reference to FIG. 3, an operation in the PON is explained.
The OLT 101 receives a main signal 122 of downstream including an ATM cell, and generates a frame signal 124 of downstream by the generator 107 for downstream frame. Particularly, the generator 107 for downstream frame receives control information 126 on the ONU from the individual ONU dealing unit 106B and information 125 on an upstream band from the controller 108 for upstream band, generates a PLOAM cell of downstream, and inserts the generated PLOAM cell into the frame signal 124 of downstream. The individual ONU dealing unit 106B exchanges information on each of the ONU's as a control signal 121 with an external operation system.
A frame signal 129 of upstream sent from each of the ONU's is terminated. A regular cell is terminated by the terminator 110 of upstream frame, and a mini slot is terminated by the terminator 111 of mini slot. The terminator 110 of upstream frame detects a PLOAM cell of upstream when the regular cell is terminated, and notifies the individual ONU dealing unit 106B of control information 130 on the ONU corresponding to the PLOAM cell. At the same time, the terminator 110 of upstream frame outputs a main signal 123 of upstream when the ATM cell besides the PLOAM cell is detected. State information 131 on a cell buffer for upstream of an ONU corresponding to the mini slot terminated by the terminator 111 of mini slot is sent to the DBA (Dynamic Bandwidth Assignment) controller 109B. Further, state information 127 corresponding to the individual ONU and information 132 on the upstream band is sent to the DBA controller 109B and the controller 108 for upstream band, and an operation of dynamic bandwidth assignment (DBA) for upstream is performed.
The ONU 103 extracts a main signal 141 of downstream including an ATM cell directed to the ONU 103 as the terminator 112 of downstream frame terminates a downstream frame signal 143. Particularly, a PLOAM cell 144 of downstream is extracted, and control information 145 on outputting the upstream cell is output to the cell generator 116 for upstream by the detector 113 for upstream band.
Further, a main signal 142 of upstream including the ATM cell is maintained in the cell buffer 114 for upstream once, and read out as information 146 on the cell based on an instruction from the cell generator 116 for upstream. A header is attached to the information 146 on the cell by the cell generator 116 for upstream, and the information 146 on the cell is output as a frame signal 149 of upstream. Information 147 on the cell buffer 114 for upstream is always monitored by the monitor 115 for buffer state, and output to the cell generator 116 for upstream as information 148 on a buffer state for mapping in the mini slot.
In the following, with reference to FIG. 4, a frame format of upstream and a downstream frame used in the PON system is explained.
In FIG. 4, the frame format 151 of downstream includes 56 ATM cells in a fixed length of 53 bytes located consecutively. Among the cells, the first cell and the 29th cell are PLOAM cells for monitoring and controlling between the OLT and the ONU.
The upstream frame format 152 includes 53 cells of 56 bytes. 56 bytes include 3 bytes of overhead and 53 bytes of ATM cells. It is also possible that the PLOAM cell is provided in an ATM cell at an arbitrary position. According to international standard ITU-T G.983.1, in a system configuration illustrated in FIG. 3, the OLT 101 manages a state of each of the ONU's 102-104 connected to the PON individually based on a state transition table of the individual ONU dealing unit in the OLT illustrated in FIG. 5.
In the following, a state transition operation of the individual ONU dealing unit in the OLT illustrated in FIG. 5 is explained.
In FIG. 5, columns arranged horizontally illustrate an initial state (OLT-IDV1), a state of measuring delay (OLT-IDV2), and an operation state (OLT-IDV3). The initial state (OLT-IDV1) illustrates a state of initializing a start operation temporally as a corresponding ONU is not started or there is a certain failure. The state of measuring delay (OLT-IDV2) illustrates a state of measuring a delay in transmission of a cell due to a transmission distance between the OLT and the ONU. The operation state (OLT-IDV3) illustrates a state of transmitting an upstream cell in timing in which the ONU compensated the delay in upstream by measuring the delay in the transmission of the cell due to the transmission distance and informing the ONU of information on the measured delay by the OLT.
Rows arranged from a top to a bottom regulate a horizontal direction, and illustrate four state transition events: instructing to start measuring delay (n), completing measuring delay (n), detecting abnormality of measuring delay (n), and detecting each of maintenance signals (LOSi, CPEi, LCDi, OAMLi, LOAi, R-INHi). In this description, n means the number of ONU. Instructing to start measuring delay (n) is an instruction issued in the initial state when the ONU is started. Completing measuring delay (n) is issued to the ONU which is measured the delay in the state of measuring delay when the delay is measured normally. Detecting abnormality of measuring delay (n) is issued to the ONU which is measured the delay in the state of measuring delay when the delay is not measured normally. Each of the maintenance signals is a signal detected and reset in the operation state in each of conditions illustrated in FIG. 6.
With reference to FIG. 5, an operation of a third ONU (n=3) is explained as an example. The third ONU which is in the initial state (OLT-IDV1) receives a state transition event of instructing to start measuring delay (n), and a state transits to the state of measuring delay (OLT-IDV2). When measuring of the delay is completed, a state transition event of completing measuring delay (n) is received, and the state transits to the operation state (OLT-IDV3). However, when measuring of the delay is failed due to a certain reason, a state transition event of detecting abnormality of measuring delay (n) is received, and the state transits to the initial state (OLT-IDV1). The individual ONU dealing unit in the OLT corresponding to the third ONU which is in the operation state (OLT-IDV3) begins to monitor each of the maintenance signals (LOSi, CPEi, LCDi, OAMLi, LOAi, R-INHi) corresponding to the third ONU. When at least one of the maintenance signals is detected, the state transits to the initial state (OLT-IDV1). After then, the individual ONU dealing unit in the OLT corresponding to the third ONU which is not in the operation state is started to go back to the operation state by a state transition event of instructing to start measuring delay (n) which occurs regularly.
An operation of the mini slot signal illustrated in FIG. 7 is explained.
The ONU which is in the operation state communicates by using the downstream frame format 151 and the upstream frame format 152 as illustrated in FIG. 4. In a certain phase of a cell, there is a case in which a certain cell is used in a slot 162 of an upstream frame 161 illustrated in FIG. 7 and the ONU sends a mini slot signal 163. In this case, when the OLT sets a phase of an upstream cell in the slot 162, a plurality of ONU's send the mini slot signals 163 in the slot 162. In this case, the mini slot signals 163 sent from the plurality of ONU's are controlled by the OLT for preventing collision. For preventing the collision, the OLT sets a phase (offset) from a beginning of the slot 162 and information on length of the mini slot signal 163 corresponding to the ONU in the ONU's individually.
In the following, as an example of operating a system using the mini slot signal illustrated in FIG. 8, control in dynamic bandwidth assignment (DBA) for upstream is explained.
The dynamic bandwidth assignment (DBA) for upstream is performed by using a mini slot signal including a function equivalent to an individual communication channel besides a regular cell from the plurality of ONU's to the OLT. By using the mini slot signal, each of the ONU's informs the OLT of a buffer state of upstream in the ONU. Then, the OLT extracts a content of the mini slot signal, and detects a buffer state in each of ONU's. It is a control method for reallocating the upstream bandwidth dynamically to each of the ONU's based on the information in the mini slot signal. For applying this control method, it is necessary that the OLT detects if the ONU can deal with the mini slot signal before controlling the bandwidth by using the mini slot.
In FIG. 8, arrangement 171 of cells in the upstream frame when the OLT provides an arbitrary band of upstream for each of the ONU's is illustrated. In the arrangement 171 of cells for upstream, ONU#1 shows a cell sent from a first ONU in a band allocated for the first ONU. ONU#2 and ONU#3 also show cells. In this state, all of the ONU's informs the OLT of a cell buffer state for upstream by using the mini slot signal constantly. For example, when it is judged that the cell buffer state for upstream in the first ONU exceeds a threshold value of the buffer determined by the OLT, the OLT temporally allocates a bandwidth wider than a present bandwidth of the upstream band. Therefore, the arrangement 171 of the cells is changed to an arrangement 172 of the cells in the upstream frame. The arrangement 172 indicates that an utilized upstream band is allocated to the first ONU.
A control method using the mini slot signal in the slot according to international standard ITU-T G.983.1 regulating the physical interface in the PON according to the related art only describes a configuration of a format of the slot. There isn't any definition about maintenance signal by the mini slot. There isn't also any definition of using the mini slot for DBA request, and of controlling method for the mini slot. Therefore, it is impossible to monitor and control a receiving state of the regular cell and the mini slot signal individually. For example, when the maintenance signal of the regular cell illustrated in FIG. 6 is used for the mini slot signal, even if only the mini slot signal operates in failure, it is judged as a state transition of the regular cell of the ONU by the individual ONU dealing unit 106B in the OLT illustrated in FIG. 5, and whole communication is suspended.
Further, FIG. 9 illustrate a state of failure of the mini slot signal in the slot 181. As illustrated, when the ONU misjudges a phase of transmission of the mini slot signal, there is a possibility of the collision with another cell or mini slot signal sent from another ONU, located before and after the mini slot signal. In such a case, there is no method of individually controlling the mini slot signal in failure by misjudging the phase of transmission, a state of the collision is maintained, and transmission of the cell or mini slot from another ONU is prevented continuously. Particularly, when the assignment of the upstream band to the ONU is controlled dynamically by using the mini slot signal, communication by all of the other ONU's is prevented by the failure of the mini slot signal of one ONU as in this case.